Higher transmission light control film

ABSTRACT

A light control film, and light collimating assemblies and liquid crystal displays incorporating such light control films are described. The light control film includes alternating transmissive and absorptive regions, where the refractive index of each transmissive region is greater than the refractive index of each absorptive region. The absorptive regions form interfaces at angles that are close to the perpendicular to the light control film. A portion of the incident light intercepting the absorptive region undergoes Total Internal Reflection, and is transmitted through the film. The axial brightness of light passing through the film is increased, the brightness is more uniform within the viewing angle, and the viewing cutoff angle is sharpened.

FIELD OF THE INVENTION

This invention generally relates to light control films and displaysincorporating same. In particular, the invention relates to lightcontrol films having improved transmission of light.

BACKGROUND

Light control film (LCF), also known as light collimating film, is anoptical film that is configured to regulate the transmission of light.Various LCFs are known, and typically include a light transmissive filmhaving a plurality of parallel grooves wherein the grooves are formed ofa light-absorbing material.

LCFs can be placed proximate a display surface, image surface, or othersurface to be viewed. At normal incidence, (i.e. 0 degree viewing angle)where a viewer is looking at an image through the LCF in a directionthat is perpendicular to the film surface, the image is viewable. As theviewing angle increases, the amount of light transmitted through the LCFdecreases until a viewing cutoff angle is reached where substantiallyall the light is blocked by the light-absorbing material and the imageis no longer viewable. This can provide privacy to a viewer by blockingobservation by others that are outside a typical range of viewingangles.

LCFs can be prepared by molding and ultraviolet radiation curing apolymerizable resin on a polycarbonate substrate. Such LCFs arecommercially available from 3M Company, St. Paul, Minn., under the tradedesignation “3M™ Filters for Notebook Computers and LCD Monitors”.

Advances in display technology have resulted in brighter, higherresolution and more energy efficient displays that consumers want. Thebrightness and resolution of a display can be reduced when an LCF ispositioned in front of the display for security or other purposes. Itwould be desirable to have an LCF which does not reduce the brightnessand resolution of a display.

SUMMARY

Generally, the present invention relates to light control films. Thepresent invention also relates to collimated lighting assemblies anddisplays incorporating collimated lighting assemblies.

In one aspect of the invention, a light control film includesalternating transmissive and absorptive regions located between a lightinput surface and a light output surface. Each absorptive regionincludes optically absorptive material selected from a pigment, a dye,or a combination; in one aspect, the material is carbon black pigment.The index of refraction of each transmissive region is greater than theindex of refraction of each absorptive region, such that the differencein the refractive indices is not less than 0.005. In one aspect, thedifference in the refractive indices is less than 0.1; in anotheraspect, the difference is between 0.007 and 0.06. A first interfaceformed between a transmissive region and an adjacent absorptive regiondefines an interface angle between the first interface and a directionperpendicular to the light output surface, such that the interface angleis not greater than 3 degrees. In one aspect, a second interface formedbetween the absorptive region and a second adjacent transmissive regionforms a second interface angle defined between the second interface anda direction perpendicular to the light output surface such that thesecond interface angle is not greater than 3 degrees.

In one aspect, light incident to the light input surface exits the lightoutput surface with a maximum brightness in a direction perpendicular tothe light output surface, and exits the light output surface at greaterthan 80% of the maximum brightness measured at any angle less than 10degrees from the direction perpendicular to the light output surface; inanother aspect, measured at any angle less than 20 degrees. In oneaspect, the light exits the light output surface at greater than 90% ofthe maximum brightness measured at any angle less than 10 degrees fromthe perpendicular; in another aspect, measured at any angle less than 20degrees.

In one aspect, the light control film includes a polar viewing cutoffangle, and light incident to the light input surface exits the lightoutput surface with a maximum brightness in a direction perpendicular tothe light output surface, and exits the light output surface at lessthan 10% of the maximum brightness measured at any angle greater thanthe polar viewing cutoff angle; in another aspect, less than 5% of themaximum brightness.

In one aspect of the invention, a collimated lighting assembly includesa light control film and a light source emitting light toward a lightinput surface of the light control film. The light control film includesa light input surface and transmissive and absorptive regions. Thetransmissive region having an index of refraction N1, and the absorptiveregion having an index of refraction N2, where N1-N2 is not less than0.005. A first interface between the transmissive region and theadjacent absorptive region makes an angle of less than 3 degrees with adirection perpendicular to the input surface. In one aspect, a secondinterface formed between the transmissive region and a second absorptiveregion forms a second interface, and the second interface makes an angleof not greater than 3 degrees with a direction perpendicular to theinput surface. In one aspect, the collimated lighting assembly can alsoinclude a prismatic film, a reflective polarizer, or a combination of aprismatic film and a reflective polarizer. The prismatic film and thereflective polarizer can be placed between the light source and thelight control film. The reflective polarizer can be laminated to thelight control film. The prismatic film can be positioned between thelight source and the reflective polarizer.

In one aspect of the invention, a liquid crystal display includes alight control film, a light source emitting light toward a light inputsurface of the light control film, and a liquid crystal display modulereceiving light from a light output surface of the light control film.The light control film includes alternating transmissive and absorptiveregions disposed laterally within a plane defined by a light inputsurface and a light output surface. The light input surface ispositioned opposite the light output surface. The index of refraction ofeach absorptive region is less than an index of refraction of eachtransmissive region by at least 0.005. A first interface between atransmissive region and a first adjacent absorptive region defines aninterface angle θ₁ measured from a direction perpendicular to the plane,wherein θ₁ is not greater than 3 degrees. In one aspect, a secondinterface formed between the transmissive region and a second absorptiveregion forms a second interface angle defined between the secondinterface and a direction perpendicular to the light output surface suchthat the second interface angle is not greater than 3 degrees.

In one aspect, the liquid crystal display can also include a prismaticfilm, a reflective polarizer, or a combination of a prismatic film and areflective polarizer. The prismatic film and the reflective polarizercan be placed between the light source and the light control film. Thereflective polarizer can be laminated to the light control film. Theprismatic film can be positioned between the light source and thereflective polarizer.

These and other aspects of the present application will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the specification reference is made to the appended drawings,where like reference numerals designate like elements, and wherein:

FIG. 1 is a cross-section view of an LCF.

FIG. 2 is a perspective view of a microstructured film article.

FIG. 3 is a perspective view of an LCF.

FIG. 4 is a perspective view of an LCF.

FIG. 5 is a schematic cross-section of an LCF.

FIG. 6 is a perspective schematic of a backlit display.

FIG. 7 is a plot of the brightness of an LCF.

FIG. 8 is a plot of the brightness of another LCF.

FIG. 9 is a plot of the brightness of another LCF.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

The present application is directed to an LCF having an increasedbrightness and uniformity of transmitted light while maintaining awell-defined viewing cutoff angle. A portion of the light entering theLCF undergoes Total Internal Reflection (TIR) within the LCF, increasingthe amount of light transmitted through the film. In one aspect, the LCFis placed between the light source and an image plane of a backlitdisplay, to improve the display brightness and uniformity, withoutreducing resolution. The included wall angles and difference of indicesof refraction between alternating absorbing and transmitting regions arekept small to accomplish these properties.

LCFs are often made to ensure that the absorptive regions absorb as muchof the incident light as possible. Highly absorptive regions minimizethe amount of light that may “leak” through these regions, and thereforecontrol the directionality and the privacy function of the LCF. Incidentlight that is reflected from these absorptive regions is also generallyminimized to reduce spurious or “ghost” images that can arise from suchreflections. LCFs can be placed between a viewer and an image plane of adisplay to limit the viewing angle of an image. Image planes can beincluded, for example, in a Liquid Crystal Display (LCD), a graphicsdisplay, and an indicia display. In some cases, LCFs can be used in aprojection display, where information in the image plane is projected toa receiving surface.

In one aspect, the relative refractive indices of the absorptive andtransmissive regions are adjusted. This adjustment may result in areduction of ghost images produced by reflections within the LCF. Whenthe refractive index of the transmissive region is less than therefractive index of the absorptive region, light incident to theinterface between them is refracted into the absorptive region andabsorbed. The refractive indexes of the two regions can be essentially“matched” so that the absorptive region refractive index is slightlyhigher than (if not equal) to the transmissive region, and reflectionsare essentially eliminated. Unfortunately, the portion of light which isabsorbed reduces the total light transmitted through the LCF, and it isdesirable to utilize a portion of this absorbed light, without alteringthe intended viewing angle

One aspect of the present invention is an LCF that is placed on the sideof the display image plane which is opposite the viewer (i.e. between alight source used to illuminate the display and the image plane of thedisplay). An LCF so positioned, minimizes the formation of ghost imagessince the LCF collimates the light into a viewing angle prior toreaching an image plane in the display. In one aspect of the invention,a portion of the light which impinges on the interface between theabsorptive and transmissive regions in the LCF reflects from theinterface and travels to the display, increasing the brightness (or“gain”) of the display within the intended viewing angle. Transmissionof light outside of the intended viewing angle is generally not desired.A reflective interface, such as a reflective metal, can cause light tobe transmitted outside of the intended viewing angle, and typically isnot acceptable.

The brightness of the display can be increased when incident lightundergoes TIR from the interface between the absorptive and transmissiveregions. Whether a light ray will undergo TIR or not, can be determinedfrom the incidence angle with the interface, and the difference inrefractive index of the materials used in the transmissive andabsorptive regions. In one aspect of the invention, the refractive indexof the absorptive region is no greater than the refractive index of thetransmissive region. In some cases, the index of refraction of thetransmissive region is greater than the index of refraction of the lightabsorptive region by at least about 0.005. In some cases, the differencebetween the indexes is less than 0.1. In some cases, the differencebetween the indexes is between 0.007 and 0.06. As used herein, “between”two numbers in a range is meant to include the endpoints of the range.For example, “between 0.007 and 0.06” is meant to include the endpoints0.007 and 0.06, and all numbers between these two endpoints.

In one aspect, the LCF can be placed between the light source and theimage display plane (e.g. LCD panel) to improve the performance ofdisplays such as automotive displays or avionics displays. Highbrightness during daylight conditions is desired for readability;however, the light from the display may produce unwanted reflections atsurfaces, such as the front wind screen. Unwanted reflections becomemore apparent in low ambient light conditions. In one aspect, thebrightness of the display is increased and unwanted reflectionsdecreased, since light remains within a controlled viewing angle,

FIG. 1 shows a cross-sectional view of an LCF 100 that includes a lightoutput surface 120 and a light input surface 110 opposite light outputsurface 120. LCF 100 includes alternating transmissive regions 130,absorptive regions 140, and an interface 150 between transmissiveregions 130 and absorptive regions 140. Transmissive regions 130 have abase width “W” disposed apart from each other by a pitch “P”, andinclude a land region “L” between absorptive regions 140 and lightoutput surface 120. Absorptive regions 140 have a base 145, a height “H”and are displaced apart from each other by pitch “P”. Interface 150forms an interface angle θ_(I) with a normal 160 to light output surface120. As described herein, by “normal” to a surface is meantperpendicular to the surface. LCF 100 includes an internal viewingcutoff angle Φ_(I) defined by the geometry of alternating transmissiveregions 130 and absorptive regions 140.

FIG. 2 shows a microstructured film article 200 comprising at least onemicrostructured surface 210, which can be used to make an LCF. In onecase, microstructured surface 210 can include a plurality of grooves 201a-201 d. As shown in FIG. 2, a continuous land layer 230 can be presentbetween the base of the grooves 220 and the opposing surface 211 ofmicrostructured film article 200. In one case, grooves 220 can extendall the way through the microstructured film article 200. In one case,microstructured film article 200 can include a base substrate layer 260which can be integrally formed with, or separately added tomicrostructured film article 200.

FIG. 3 shows an LCF 300 wherein grooves 201 a-201 d of FIG. 2 have beenrendered light-absorbing by being filled with a light absorbing material350. Light absorbing material 350 in the shape of the recess of the(e.g. groove) microstructure is herein referred to as absorptive region140.

FIG. 4 shows an LCF 400 that further includes an optional cover film 470that can be the same, or different than, base substrate layer 260.Optional cover film 470 can be bonded to the microstructured surfacewith an adhesive 410. Adhesive 410 can be any optically clear adhesive,such as a UV-curable acrylate adhesive, a transfer adhesive, and thelike. LCF 400 also includes light input surface 110 and light outputsurface 120 opposite light input surface 110, defining a plane. It is tobe understood that for the purposes of describing the invention herein,LCF 400 is positioned such that light input surface 110 is disposedproximate to a base 145 of absorptive region 140, however, light inputsurface 110 can also be disposed opposite base 145. In other words, LCF400 can be positioned such that base 145 is closer to a light source(not shown) that injects light into light input surface 110, or it canalso be positioned such that base 145 is closer to a display plane (notshown) that receives light from light output surface 120.

As shown in FIGS. 3 and 4, transmissive regions 130 between absorptiveregions 140 have an included wall angle θ_(T), a transmissive regionbase width “W”, an effective height “H”, a pitch “P”, and a polarviewing cutoff angle Φ_(P). Included wall angle θ_(T) is two times theinterface angle θ_(I) shown in FIG. 1 for symmetric absorptive regions.In one case, interface angle θ_(I) can be different for each interface150, and included wall angle θ_(T) is equal to the sum of the interfaceangles θ_(I) on each side of absorptive region 140, for an unsymmetricalabsorptive region. Polar viewing cutoff angle Φ_(P) can be determined byapplying Snell's law to the rays defining the internal viewing cutoffangle Φ_(I), using the indices of refraction of optional cover film 470,adhesive 410, transmissive regions 130, base substrate layer 260, andthe material that LCF 400 is immersed in (typically air). Polar viewingcutoff angle Φ_(P) is equal to the sum of a polar viewing cutoff halfangle Φ₁ and a polar viewing cutoff half angle Φ₂ each of which aremeasured from the normal to light input surface 110. In some cases,polar viewing cutoff angle Φ_(P) can be symmetric, and polar viewingcutoff half angle Φ₁ is equal to polar viewing cutoff half angle Φ₂. Insome cases, polar viewing cutoff angle Φ_(P) can be asymmetric, andpolar viewing cutoff half angle Φ₁ is not equal to polar viewing cutoffhalf angle Φ₂. For the purposes of this disclosure, an angle “Φ” shownin FIG. 4 and measured from the normal to light input surface 110 alongthe direction shown, is herein referred to as a “polar viewing angle”.The polar viewing angle Φ can range from 0° (i.e. normal to light inputsurface 110) to 90° (i.e. parallel to light input surface 110).

The material properties of transmissive regions 130, included wall angleθ_(T), pitch “P”, and transmissive region base width “W” can impactlight transmission through LCF 400. LCFs can have relatively largeincluded wall angles, such as greater than 10 degrees or more. Largerwall angles increase the width of the light absorbing regions, therebydecreasing transmission at normal incidence. Smaller wall angles arepreferred, such as less than 10 degrees, so that the transmission oflight at normal incidence can be made as large as possible.

In one aspect, the present invention can be directed to LCFs where theincluded wall angle can be not greater than 6°. In one aspect, theincluded wall angle can be not greater than 5°, such as less than 5°,4°, 3°, 2°, 1° or 0.1°. As described herein, the included wall angle canbe related to the interface angle for symmetric and asymmetricabsorptive regions. As such, in one aspect, the interface angle can be3°, or not greater than 3°, for example not greater than 2.5°, 2°, 1°,or 0.1°. Smaller wall angles can form grooves having a relatively highaspect ratio (H/W) at a smaller pitch “P”, and can provide a sharperimage cutoff at lower viewing angles. In some cases, the transmissiveregions have an average height, “H”, and an average width at its widestportion, “W”, and H/W is at least 1.75. In some cases, H/W is at least2.0, 2.5, 3.0 or greater.

LCFs can be made to have any desired polar viewing cutoff angle. In oneaspect, the polar viewing cutoff angle ranges from 40° to 90° or evenhigher. The polar viewing cutoff angle Φ_(P), can be determined asdiscussed elsewhere by the parameters “θ_(I)”, “H”, “W”, “P”, and theindices of the LCF materials. In some cases, it can also be useful todefine a “functional polar viewing angle” which includes lighttransmitted through the LCF at angles larger than the polar viewingcutoff angle. For example, light that intercepts the absorptive regionsat angles slightly larger than the internal viewing cutoff angle Φ_(I)can “bleed through” the thinnest portions of the absorptive region (i.e.partially transmit through the top and bottom of the light absorbingregions represented as trapezoids shown in FIG. 1). The functional polarviewing angle can be defined as the angle at which the brightnessdecreases to a small percentage, for example 10%, 5% or even less, ofthe axial brightness.

FIG. 5 shows an LCF 500 according to one aspect of the presentinvention. The light transmission of LCF 500 is greater than the lighttransmission through prior art LCFs, since some of the light impingingon absorptive regions 140 is reflected by TIR. LCF 500 includestransmissive regions 130 comprising a material having index ofrefraction N1, and absorptive regions 140 comprising a material havingan index of refraction N2 which is not greater than N1. The criticalangle, θ_(c) (not shown) for the interface is θ_(c)=arcsin(N2/N1). Lightrays impinging on interface 150 at angles greater than θ_(c), undergoTIR at interface 150. Light rays impinging on interface 150 at anglesless than θ_(c) are absorbed by absorptive regions 140.

FIG. 5 shows three light rays, ABC, DEF and GH which enter transmissiveregion 130 through light input surface 110. Light ray ABC enterstransmissive region 130 within internal viewing cutoff angle Φ_(I),intercepts absorptive region 140 at angle of incidence θ_(i) greaterthan θ_(c), and undergoes TIR to exit through light output surface 120.In a similar manner, light ray DEF enters transmissive region 130outside of internal viewing cutoff angle Φ_(I), intercepts absorptiveregion 140 at angle of incidence θ_(i) greater than θ_(c), and undergoesTIR to exit through light output surface 120. Light ray GH enterstransmissive region 130 outside internal viewing cutoff angle Φ_(I),intercepts absorptive region 140 at angle of incidence θ_(i) less thanθ_(c), and is absorbed by absorptive region 140. The included wall angleθ_(T), transmissive index N1, and absorptive index N2, are adjustableparameters for control of the transmission of light through light outputsurface 120. Selection of these parameters can cause some of the lightwhich would otherwise be absorbed by absorptive region 140, to insteadbe reflected from interface 150 and directed through the output surfacewithin the intended internal viewing cutoff angle Φ_(I).

As the index difference between the absorptive regions and thetransmissive regions increases, critical angle θ_(c) decreases, and moreof the light impinging on the interface is reflected from the interface.The LCF has higher brightness (or gain), but can result in the undesiredtransmission of light through the output surface of the LCF at anglesthat are larger than the intended viewing cutoff angle. In some cases,it can be desirable to limit the difference in the relative refractiveindexes, in order to control these unwanted reflections. In one aspect,the present invention is directed to LCFs comprising materials that havesmall differences in refractive index, such as between 0.005 and 0.1,and small interface wall angles, such as not greater than 3°, or between0.1° and 3°.

In some cases, light absorbing materials for the light absorbing regionsin LCFs can be any suitable material that functions to absorb or blocklight at least in a portion of the visible spectrum. In some cases, thelight absorbing material can be coated or otherwise provided in groovesor indentations in a light transmissive film to form light absorbingregions. In some cases, light absorbing materials can include a blackcolorant, such as carbon black. In one embodiment, the carbon black canbe a particulate carbon black having a particle size less than 10microns, for example 1 micron or less. In one embodiment the carbonblack can have a mean particle size of less than 1 micron. In somecases, carbon black, another pigment or dye, or combinations thereof canbe dispersed in a suitable binder. In some cases, light absorbingmaterials can include particles or other scattering elements that canfunction to block light from being transmitted through the lightabsorbing regions.

In one aspect, the light absorbing region can comprise substantially thesame polymerizable resin composition as the light transmissive material.In this embodiment, the refractive index of the light absorbing regionmaterial can be no greater than the refractive index of the lighttransmissive region material. In some cases, the amount of colorant,such as carbon black, is at least about 1 wt-% and no greater than about10 wt-% of the total light absorbing region material composition. Insome cases, from about 2% to about 5% carbon black by weight can bemixed with an absorptive region resin material to sufficiently absorbincident light. The refractive index of carbon black is higher than 1.5,so in some cases, a low refractive index resin can be mixed with thecarbon black to maintain a desired refractive index difference betweenabsorptive and transmissive regions.

Reflections at the light transmissive region/light absorbing regioninterface can be controlled by mismatching the relative index ofrefraction of the light transmissive material and the index ofrefraction of the light absorbing material over at least a portion ofthe spectrum, for example the human visible spectrum. In some cases, theindex of refraction of the cured transmissive regions (N1) is greaterthan the index of refraction of the cured light absorptive regions (N2)by at least about 0.005. In some cases, the index of refractiondifference, (N1−N2) is not less than 0.005, or, (N1−N2) is greater thanor equal to 0.005. In some cases, the difference between the indexes(N1−N2) can be less than 0.1, and can be between 0.007 and 0.06.

In one aspect, the LCF includes a plurality of light absorbing regions.In some embodiments, the light absorbing regions can be a plurality ofchannels, as shown elsewhere in the description. In some cases, the LCFcan include a plurality of columns such as shown in FIG. 2b of U.S. Pat.No. 6,398,370 (Chiu et al.). In some cases, the LCF described herein canbe combined with a second LCF, as also described in U.S. Pat. No.6,398,370. In other embodiments, the light absorbing regions arecolumns, posts, pyramids, cones and other structures that can addangular-dependent light transmitting or light blocking capabilities to afilm.

The polymerizable resin can comprise a combination of a first and secondpolymerizable component selected from (meth)acrylate monomers,(meth)acrylate oligomers, and mixtures thereof. As used herein,“monomer” or “oligomer” is any substance that can be converted into apolymer. The term “(meth)acrylate” refers to both acrylate andmethacrylate compounds. In some cases, the polymerizable composition cancomprise a (meth)acrylated urethane oligomer, (meth)acrylated epoxyoligomer, (meth)acrylated polyester oligomer, a (meth)acrylated phenolicoligomer, a (meth)acrylated acrylic oligomer, and mixtures thereof. Thepolymerizable resin can be a radiation curable polymeric resin, such asa UV curable resin. In some cases, polymerizable resin compositionsuseful for the LCF of the present invention can include polymerizableresin compositions such as are described in U.S. Publication No.2007/0160811 (Gaides et al.), to the extent that those compositionssatisfy the index and absorption characteristics herein described.

A microstructure-bearing article (e.g. microstructured film article 200shown in FIG. 2) can be prepared by a method including the steps of (a)preparing a polymerizable composition; (b) depositing the polymerizablecomposition onto a master negative microstructured molding surface in anamount barely sufficient to fill the cavities of the master; (c) fillingthe cavities by moving a bead of the polymerizable composition between apreformed base and the master, at least one of which is flexible; and(d) curing the composition. The deposition temperature can range fromambient temperature to about 180° F. (82° C.). The master can bemetallic, such as nickel, chrome- or nickel-plated copper or brass, orcan be a thermoplastic material that is stable under the polymerizationconditions, and has a surface energy that allows clean removal of thepolymerized material from the master. One or more of the surfaces of thebase film can optionally be primed or otherwise be treated to promoteadhesion of the optical layer to the base.

The polymerizable resin compositions described herein are suitable foruse in the manufacture of other light transmissive and/ormicrostructured articles including for example brightness enhancingfilms and the like. The term “microstructure” is used herein as definedand explained in U.S. Pat. No. 4,576,850 (Martens). Microstructures aregenerally discontinuities such as projections and indentations in thesurface of an article that deviate in profile from an average centerline drawn through the microstructure such that the sum of the areasembraced by the surface profile above the center line is equal to thesum of the areas below the line, the line being essentially parallel tothe nominal surface (bearing the microstructure) of the article. Theheights of the deviations will typically be about +/−0.005 to +/−750microns, as measured by an optical or electron microscope, through arepresentative characteristic length of the surface, e.g., 1-30 cm. Theaverage center line can be plano, concave, convex, aspheric orcombinations thereof. Articles where the deviations are of low order,e.g., from +/−0.005, +/−0.1 or, +/−0.05 microns, and the deviations areof infrequent or minimal occurrence, i.e., the surface is free of anysignificant discontinuities, can be considered to have an essentially“flat” or “smooth” surface. Other articles have deviations are ofhigh-order, e.g., from +/−0.1 to +/−750 microns, and attributable tomicrostructure comprising a plurality of utilitarian discontinuitieswhich are the same or different and spaced apart or contiguous in arandom or ordered manner.

The chemical composition and thickness of the base material can dependon the requirements of the product that is being constructed. That is,balancing the needs for strength, clarity, optical retardance,temperature resistance, surface energy, adherence to the optical layer,among others. In some cases, the thickness of the base layer can be atleast about 0.025 millimeters (mm) and can be from about 0.1 mm to about0.5 mm.

Useful base materials include, for example, styrene-acrylonitrile,cellulose acetate butyrate, cellulose acetate propionate, cellulosetriacetate, polyether sulfone, polymethyl methacrylate, polyurethane,polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylenenaphthalate, copolymers or blends based on naphthalene dicarboxylicacids, polyolefin-based material such as cast or orientated films ofpolyethylene, polypropylene, and polycyclo-olefins, polyimides, andglass. Optionally, the base material can contain mixtures orcombinations of these materials. In one case, the base may bemulti-layered or may contain a dispersed component suspended ordispersed in a continuous phase.

In one aspect, examples of base materials include polyethyleneterephthalate (PET) and polycarbonate (PC). Examples of useful PET filmsinclude photograde polyethylene terephthalate, available from DuPontFilms of Wilmington, Del. under the trade designation “Melinex 618”.Examples of optical grade polycarbonate films include LEXAN®polycarbonate film 8010, available from GE Polymershapes, Seattle Wash.,and Panlite 1151, available from Teijin Kasei, Alpharetta Ga.

Some base materials can be optically active, and can act as polarizingmaterials. A number of bases, also referred to herein as films orsubstrates, are known in the optical product art to be useful aspolarizing materials. Polarization of light through a film can beaccomplished, for example, by the inclusion of dichroic polarizers in afilm material that selectively absorbs passing light. Light polarizationcan also be achieved by including inorganic materials such as alignedmica chips or by a discontinuous phase dispersed within a continuousfilm, such as droplets of light modulating liquid crystals dispersedwithin a continuous film. As an alternative, a film can be prepared frommicrofine layers of different materials. The polarizing materials withinthe film can be aligned into a polarizing orientation, for example, byemploying methods such as stretching the film, applying electric ormagnetic fields, and coating techniques.

Examples of polarizing films include those described in U.S. Pat. No.5,825,543 (Ouderkirk et al.); U.S. Pat. No. 5,783,120 (Ouderkirk etal.); U.S. Pat. No. 5,882,774 (Jonza et al.); U.S. Pat. No. 5,612,820(Shrenk et al.) and U.S. Pat. No. 5,486,949 (Shrenk et al.). The use ofthese polarizer films in combination with prismatic brightnessenhancement film has been described, for example, in U.S. Pat. No.6,111,696 (Allen et al.) and U.S. Pat. No. 5,828,488 (Ouderkirk et al.).Films available commercially are multilayer reflective polarizer filmssuch as Vikuiti™ Dual Brightness Enhancement Film “DBEF”, available from3M Company.

The base materials listed herein are not exclusive, and as will beappreciated by those of skill in the art, other polarizing andnon-polarizing films can also be useful as the base for the opticalproducts of the invention. These base materials can be combined with anynumber of other films including, for example, polarizing films to formmultilayer structures. The thickness of a particular base can alsodepend on the desired properties of the optical product.

FIG. 6 shows a perspective schematic of a backlit display 600 accordingto one exemplary aspect the present invention. Backlit display 600includes an LCF 630 to define a polar viewing cutoff angle Φ_(P) oflight leaving an output surface 690 of LCF 630. Polar viewing cutoffangle Φ_(P) includes a polar viewing cutoff half angle Φ₁ and a polarviewing cutoff half angle Φ₂ measured from a normal 680 to light outputsurface 690, as described elsewhere. LCF 630 includes transmissiveregions 640 and absorptive regions 650 as described elsewhere. Backlitdisplay 600 includes a light source 610 configured to transmit lightthrough LCF 630, through an image plane 620, such as an LCD panel, andon to a viewer 695. The viewing angle at which the brightness is amaximum, can depend on whether the polar viewing cutoff angle issymmetric about normal 680 or is asymmetric, as described elsewhere. Inone aspect, the brightness of backlit display 600 can be greatest alongnormal 680 (referred to as the “axial brightness”), and decrease as theviewing angle is increased. For asymmetric polar viewing cutoff angles,the maximum brightness may not be coincident with normal 680. Backlitdisplay 600 can also include an optional brightness enhancement film 660and a reflective polarizer film 670 to further improve the brightnessand uniformity of the display. Brightness enhancement film can be aprism film, such as Vikuiti™ Brightness Enhancement Film “BEF” or ThinBrightness Enhancement Film “TBEF”, available from 3M Company.Reflective polarizer film 670 can be a multilayer optical film, such asVikuiti™ Dual Brightness Enhancement Film “DBEF”, available from 3MCompany). Brightness enhancement film 660 and reflective polarizer film670, if included, can be positioned as shown in FIG. 6.

The present invention should not be considered limited to the particularmodeling and examples described herein, but rather should be understoodto cover all aspects of the invention as fairly set out in the attachedclaims. Various modifications, equivalent processes, as well as numerousstructures to which the present invention can be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification. Theforegoing description can be better understood by consideration of theembodiments shown by the modeling results and examples that follow.

Ray-Trace Modeling of LCF

The performance of the LCF was modeled using an optical raytraceprogram. The optical raytrace program provides results comparable topublic commercial raytrace software, such as TracePro® (available fromLambda Research Corp., Littleton Mass.), and LightTools® (available fromOptical Research Associates, Pasadena Calif.).

The optical properties of BEF and LCF were inputs into the program, andthe physical dimensions and structures were input as shown below. Theabsorption coefficient of the black resin was calibrated with the actualattenuation of light incident at 37° of a carbon-filled blackphoto-polymerizable mixed acrylate resin (substantially the same as the“high index black resin” presented in as Mixture 3 in Table 3). Themodel corresponded to an arrangement similar to FIG. 6, where lightsource 610 was a lambertian light source, brightness enhancement film660 was the Vikuiti™ Brightness Enhancement Film BEF-II design,reflective polarizer film 670 was not used, and LCF 630 was configuredas shown in FIG. 4 as LCF 400 (i.e. with 0.1 mm thick polycarbonatecover film 470, 0.1 mm thick polycarbonate base substrate layer 260, and0.025 mm thick adhesive 410).

Parallel rays at a viewing angle Φ were traced from image plane 620toward the lambertian light source 610, and the luminance (brightness)was recorded. The process was repeated for viewing angles from 0° to 90°to generate each of the plots. The program accounted for the attenuationby reflection and absorption of the initial ray traversing through thematerials and interfaces, until it intercepted the source surface. Theattenuation provided a factor for multiplying the surface brightness,and resulted in the brightness at the viewing direction of the initialray. Plots were generated that show the intensity vs. viewing angle in aplane perpendicular to the film surface and along the groove direction(horizontal plane) and in a plane perpendicular to the film surface andperpendicular to the groove direction (vertical plane). The plots shownin FIGS. 7-9 include data from both viewing directions. The brightnessprofile in the horizontal plane is labeled “along groove”.

TABLE 1 Model input parameters common to Examples 1-3 Material, propertyValue (units) PC, index 1.583 PC, absorption coefficient 0.005 (1/mm)Adhesive, index 1.52 Adhesive, absorption coefficient 0 Transmissiveregion, index 1.54 Transmissive region, absorption coefficient 0.005(1/mm) Absorptive region, absorption coefficient 129 (1/mm) “H”, heightof absorptive region 0.146 mm “L”, land thickness 0.015 mm “P”, pitch0.070 mm Φ_(P), polar viewing cutoff angle 60 degrees

Example 1 Model with Interface Wall Angle=0.1°

The interface wall angle input to the model was set to a value of 0.1°.The resulting width “W” was 0.0523 mm to result in the 60° polar viewingcutoff angle. The index of the absorptive region was set equal to theindex of the transmissive region, and the brightness was calculated atseveral polar viewing angles by the method described elsewhere. Theindex was decreased by 0.01 and the calculation was repeated until thedifference in the indices was 0.1. The brightness values generated theseries of plots shown in FIG. 7 for a 0.1° interface wall angle. Asshown in FIGS. 7-9, the plot corresponding to matched index values waslabeled “A”, and the index difference increased by 0.01 incrementsmoving to the right, ending at the index difference 0.1 represented bythe plot labeled “K”.

Example 2 Model with Interface Wall Angle=1.0°

The same procedure as in Example 1 was used, with the exception that theinterface wall angle input to the model was set to a value of 1.0°, andthe resulting width “W” was 0.0571 mm to result in the 60° polar viewingcutoff angle. The brightness values generated the series of plots shownin FIG. 8 for a 1.0° interface wall angle.

Example 3 Model with Interface Wall Angle=3.0°

The same procedure as in Example 1 was used, with the exception that theinterface wall angle input to the model was set to a value of 3.0°, andthe resulting width “W” was 0.0673 mm to result in the 60° polar viewingcutoff angle. The brightness values generated the series of plots shownin FIG. 9 for a 3.0° interface wall angle.

Representative Values for Axial Brightness and Brightness at ViewingAngle Φ

The polar viewing half angle (PVHA) at which the brightness was 70%, 80%and 90% of the axial brightness (AB) was calculated from the modeleddata for selected interface angles θ_(I) and refractive indexdifferences (N1−N2). These values are represented at Table 2.

TABLE 2 Polar viewing half angle for selected percentage values of axialbrightness PVHA at PVHA at PVHA at θ_(I), AB, 90% AB, 80% AB, 70% AB,degrees (N1 − N2) (cd/m2) degrees degrees degrees 0.1 0 124.48 3.6 6.710.3 0.1 0.05 126.49 22.2 22.6 23 0.1 0.1 126.25 26 30.6 32.3 1.0 0119.85 4.7 7.8 11.1 1.0 0.05 133.01 21 21.3 21.6 1.0 0.1 132.7 22 27.930 3.0 0 109.28 7.2 10.1 13 3.0 0.05 143.99 17.4 18.2 18.5 3.0 0.1143.72 19.1 22.5 24

Preparation and Evaluation of LCFs Using UV Curable Materials

LCFs were made and evaluated according to the procedures describedbelow. The following list of materials was used, except as otherwisenoted. Four mixtures of radiation curable resins used in theseembodiments are shown in Table 3.

PET (Melinex 618, DuPont Films, Wilmington, Del.)—photogradepolyethylene terephthalate; chemically primed on one side.PC (LEXAN® 8010, GE Polymershapes, Seattle Wash.)—photogradepolycarbonate filmSR 285 (Sartomer, Exton Pa.)—tetrahydrofurfuryl acrylateSR 351 (Sartomer, Exton Pa.)—trimethylolpropane triacrylate (TMPTA)SR 602 (Sartomer, Exton Pa.)—bisphenol A diacrylate with about fourmoles of ethoxylationSR 339 (Sartomer, Exton Pa.)—2-phenoxyethyl acrylateSR 238 (Sartomer, Exton Pa.)—1,6-hexanediol diacrylatePhotomer 6010 (Cognis, Cincinnati Ohio)—aliphatic urethane diacrylatePhotomer 6210 (Cognis, Cincinnati Ohio)—aliphatic urethane diacrylateEbecryl 350 (UCB Chemicals, Smyrna Ga.)—acrylated silicone9B385 (Penn Color, Doylestown Pa.)—carbon black UV curable pasteSR 9003 (Sartomer, Exton Pa.)—propoxylated(2) neopentyl glycoldiacrylateTPO (BASF, Florham Park, N.J.)—Lucirin® TPO photoinitiatorDarocur 1173 (Ciba Specialty Chemicals, Tarrytown N.Y.)—photoinitiatorIrgacure 369 (Ciba Specialty Chemicals, Tarrytown N.Y.)—photoinitiatorIrgacure 819 (Ciba Specialty Chemicals, Tarrytown N.Y.)—photoinitiator

TABLE 3 UV polymerizable resin mixture compositions Refrac- SampleMixture Compositions tive Description (all percentages are by weight)Index^(d) Mixture 1 94% 5% 1% — — 1.498 Low Index Photomer SR-285Darocur (1.488) “Clear” 6010 1173 Resin Mixture 2^(a) 45% 36.7% 7.1%7.1% 4.1% 1.512 High Index Photomer SR-602 SR-238 SR-351 SR-339 (1.496)“Clear” 6010 Resin Mixture 3^(b) 67% 20% 10% — — (1.514) High IndexPhotomer 9B385 SR-285 “Black” 6210 Resin Mixture 4^(c) 73% 15% 5% SR-4.5% — (1.447) Low Index Ebecryl 9B385 9003 SR-285 “Black” 350 Resin^(a)Mixture 2 had 0.1% TPO and 0.35% Darocur 1173 photoinitiators added.^(b)Mixture 3 had 1% each of Irgaucre 369, Irgacure 819, and Darocur1173 added. ^(c)Mixture 4 had 1.5% Darocur 1173 and 1% Irgacure 819added. ^(d)Calculated refractive index appears in parenthesis, otherwiseit was measured.

Refractive Index Determination of Cured Resins

The resins of Mixture 1 and Mixture 2 were separately mixed, and coatedbetween a 0.008 inch (0.20 mm) PC film and an unprimed 0.005 inch PETfilm using a precision laboratory drawdown coater (manufactured byChemInstruments) to a thickness of approximately 50 The resultinglaminate was cured using UV radiation (1 pass, 25 feet per minute,one-side exposure with two Fusion D bulbs), and the PET coversheet wasremoved. The refractive index of the photopolymerized resins weremeasured using a Metricon Model 2010 Prism Coupler System (MetriconCorp, Pennington N.J.) at a wavelength of 633 nm. Due to the presence ofthe carbon black in Mixtures 3 and 4, this method could not be used forthose mixtures.

The calculated refractive index of the resins of Mixtures 1 through 4were each determined from published refractive index values for each ofthe individual components at a wavelength of 512 nm. A linear mixingrule was used. The increase in refractive index due to the addition ofcarbon black added, was 0.009 for every 1% carbon black added by weightto each mixture.

Preparation of Microstructured Films

Microstructured films were made by molding and ultraviolet (UV) lightcuring the compositions of Mixture 1 and Mixture 2 of Table 3 on eithera 0.007 inch (0.178 mm) on primed PET film or a 0.007 inch (0.178 mm) PCfilm. For these structured films, a cylindrically-shaped metal roll withfinely detailed channels cut into its outer surface served as the mold.The resinous mixture was first coated onto either the PET or the PCsubstrate film, and then pressed firmly against the metal roll in orderto completely fill the mold. Upon polymerization the structured film wasremoved from the mold. The resulting structure in the cured resin was aseries of evenly spaced channels, each having a nominally trapezoidalcross-section. The cured resin channels were about 48 microns wide (attheir narrowest), about 146 microns deep, and spaced at about a 70micron pitch. The included wall angle, θ_(T), was about 3.6°. FIG. 2 isrepresentative of such a microstructured film.

Preparation of Light Collimating Films

Light collimating films were made by filling the gaps between thetransparent channels of the microstructured film using each of the resincompositions of Mixture 3 and Mixture 4 listed in Table 3. Excessblack-containing resin was wiped from the surfaces of the transparentchannels. The carbon black filled channels were then cured using UVradiation, resulting in a light collimating film similar to that shownin FIG. 3. Each light collimating film was laminated to a 0.008 inch(0.20 mm) PC coversheet film using a UV-curable adhesive (UVX4856available from Toagosei Co. Ltd, Tokyo, Japan). FIG. 4 is representativeof such a light collimating film. The polar viewing cutoff angle Φ_(P)for this light collimating film was 60°.

Example 4

A microstructured film was made using the “Mixture 1” low index clearresin composition of Table 3, on PC film as described above. Themicrostructured film was then filled with the “Mixture 4” low indexblack resin composition of Table 3, UV cured, and laminated to PC filmusing the UV curable adhesive and methods described above, to result ina light collimating film.

Example 5

A microstructured film was made using the “Mixture 2” high index clearresin composition of Table 3, on PET film as described above. Themicrostructured film was then filled with the “Mixture 4” low indexblack resin composition of Table 3, UV cured, and laminated to PC filmusing the UV curable adhesive and method described above, to result in alight collimating film.

Comparative Example #1

A microstructured film was made using the “Mixture 1” low index clearresin composition of Table 3, on PC film as described above. Themicrostructured film was then filled with the “Mixture 3” high indexblack resin composition of Table 3, UV cured, and laminated to PC filmusing the UV curable adhesive and method described above, to result in alight collimating film.

Luminance Measurements

An Eldim 80 Conoscope (Eldim Corp, France) was used to measure theluminance (brightness) profiles of a backlight incorporating the LCFs ofExample 4, Example 5, and Comparative Example 1. A Sharp 7″ TFT LCDmodule (Model # LQ070T5CRQ1, available from Sharp Electronics, MahwahN.J.) was modified to include a sheet of Vikuiti™ Brightness EnhancementFilm (BEF III-5T, available from 3M Company). Brightness data were takenwith the placement of a light collimating film between the BEF and therear polarizer of the LCD panel (similar to the construction given atFIG. 6). The results from these measurements are shown at Table 4. Theaxial brightness was the brightness measured perpendicular to thesurface of the LCD panel. The polar viewing half angle (PVHA) at whichthe brightness was 70%, 80% and 90% of the axial brightness (AB) wasmeasured, and the PVHA at which the brightness was 5% of the AB was alsomeasured. The PVHA at 5% of the AB designated a functional polar viewingangle as described elsewhere. A summary of these results are shown atTable 4.

TABLE 4 Axial brightness and polar ½- view angle data of LightCollimating Films PVHA at PVHA at PVHA at PVHA at Sample AB 90% AB, 80%AB, 70% AB, 5% AB, Description (cd/m²) degrees degrees degrees degreesExample 4 243 8.0 11.0 13.0 30.0 Example 5 256 8.5 13.5 16.5 32.4Comparative 192 4.0 6.5 8.5 29.6 Example #1

The light collimating films of Example 4 and Comparative Example 1differ only in the black resin composition and refractive index. Thelight collimating film of Example 5 used a clear resin that was slightlyhigher in refractive index than the clear resin used in Example 4.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe foregoing specification and attached claims are approximations thatcan vary depending upon the desired properties sought to be obtained bythose skilled in the art utilizing the teachings disclosed herein.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations can besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present disclosure. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisdisclosure be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A collimated lighting assembly, comprising: alight control film, comprising: a light input surface; transmissive andabsorptive regions, the transmissive region having an index ofrefraction N1, and the absorptive region having an index of refractionN2, where N1−N2 is not less than 0.005, wherein a first interfacebetween the transmissive region and the absorptive region makes an anglenot greater than 3 degrees with a direction perpendicular to the inputsurface; and a light source emitting light toward the light inputsurface.
 2. The collimated lighting assembly of claim 1, furthercomprising a prismatic film disposed between the light source and thelight control film.
 3. The collimated lighting assembly of claim 1,further comprising a reflective polarizer disposed between the lightsource and the light control film.
 4. The collimated lighting assemblyof claim 3, wherein the reflective polarizer is laminated to the lightcontrol film.
 5. The collimated lighting assembly of claim 3, furthercomprising a prismatic film disposed between the light source and thereflective polarizer.
 6. The light control film of claim 1, wherein thetransmissive region has a second interface with a second absorptiveregion, and the second interface makes an angle of not greater than 3degrees with the direction perpendicular to the input surface.
 7. Aliquid crystal display, comprising: a light control film, comprising:alternating transmissive and absorptive regions disposed laterallywithin a plane defined by a light input surface and a light outputsurface opposite the light input surface, an index of refraction of eachabsorptive region being less than an index of refraction of eachtransmissive region by at least 0.005; a first interface between atransmissive region and a first adjacent absorptive region defining aninterface angle θ₁ measured from a direction perpendicular to the planeof the film, wherein θ₁ is not greater than 3 degrees; a light sourceemitting light toward the light input surface; and a liquid crystaldisplay module receiving light from the light output surface.
 8. Theliquid crystal display of claim 7, further comprising a prismatic filmdisposed between the light source and the light control film.
 9. Theliquid crystal display of claim 7, further comprising a reflectivepolarizer disposed between the light source and the light control film.10. The liquid crystal display of claim 9, wherein the reflectivepolarizer is laminated to the light control film.
 11. The liquid crystaldisplay of claim 9, further comprising a prismatic film disposed betweenthe light source and the reflective polarizer.
 12. The light controlfilm of claim 7, wherein the transmissive region has a second interfacewith a second adjacent absorptive region, and an interface angle θ2defined by the second interface and a direction perpendicular to thelight output surface, where θ2 is not greater than 3 degrees.